The overall objective of this work is to eludicate some of the interactions between feeding schedule and small intestinal function and to gain further understanding of the regulation of gastrointestinal function and the nature of biorhythms. More specifically: 1) to determine how the level of activity of brush border enzymes and transport systems are altered within the rhythm period by analysis of the rhythm in different regions of the gut, cytological evaluation of the epithelial cell surface and evaluaton of the intraluminal degradation of enzymes, 2) to determine at what stage in the life cycle these functions develop diurnal rhythmicity and whether a spontaneous rhythm exists independently of direct ingestion by determination of the presence of rhythmicity in rats of various ages, both in utero and after birth, and 3) to elucidate which component(s) of the feeding schedule are the cue(s) of the diurnal rhythms and which component(s) of the alimentary canal are involved in the internal mediation of the cue by determination of the relation between the fetal rhythms and those of the dams feeding schedule and by manipulation of the route of feeding and the diet in older animals.